Poly , glass ionomer

Resin-Modified Glass—Ionomer Cements. Resin-modified glass—ionomer cements are based on poly(alkeonic acid) systems that have... 

Resin-modified glass—ionomer lining and restorative materials add a multifunctional acidic monomer to the poly(acryhc acid) [9003-01 Hquid component of the system. Once the glass powder and Hquid are mixed, setting can proceed by the acid—glass—ionomer reaction or the added monomer can be polymerized by a free-radical mechanism to rapidly fix the material in place (74,75). The cured material stiH retains the fluoride releasing capabiHties of a glass—ionomer. 

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

Water occurs in glass-ionomer and related cements in at least two different states (Wilson McLean, 1988 Prosser Wilson, 1979). These states have been classified as evaporable and non-evaporable, depending on whether the water can be removed by vacuum desiccation over silica gel or whether it remains firmly bound in the cement when subjected to such treatment (Wilson Crisp, 1975). The alternative descriptions loosely bound and tightly bound have also been applied to these different states of water combination. In the glass-poly(acrylic acid) system the evaporable water is up to 5 % by weight of the total cement, while the bound water is 18-28 % (Prosser Wilson, 1979). This amount of tightly bound water is equivalent to five or six molecules of water for each acid group and associated metal cation. Hence at least ten molecules of water are involved in the hydration of each coordinated metal ion at a carboxylate site. 

Wilson, A. D. Ellis, J. (1989). Poly-vinylphosphonic acid and metal oxide or cermet or glass-ionomer cements. British Patent Application 2, 219, 289A. 

Hill, R. G., Wilson, A. D. Warrens, C. P. (1989). The influence of poly(acrylic acid) molecular weight on the fracture toughness of glass-ionomer cements. Journal of Materials Science, 24, 363-71. 

Nicholson, J. W., Braybrook, J. H. Wasson, E. A. (1991). The biocompatibility of glass-poly(alkenoate) (glass-ionomer) a review. Journal of Biomedical Science, Polymer Edition, 2, 277-85. 

Wilson, A. D. Crisp, S. (1980). Dental cement containing poly(carboxylic acid), chelating agent and glass ionomer powder. US Patent 4,209,434. 

The main line of development now lies with its successor, the glass-ionomer cement, which uses a similar glass, but in which phosphoric acid is replaced by poly(acrylic acid) this cement is more resistant to acid erosion and staining and has the great advantage of adhesion to tooth material. 

The glasses are similar to those used in glass-ionomer cements but their reactivity towards acids has to be less, as orthophosphoric add is a stronger acid than the poly(alkenoic acid)s. The consequence is that the Al/Si ratio, which determines reactivity, is lower than in the glass-ionomer cement glasses. 

Ellis, J., Anstice, M. Wilson, A. D. (1991). The glass polyphosphonate cement a novel glass-ionomer cement based on poly(vinylphosphonic acid). Clinical Materials, 7, 341-6. 

In another study, oscillating rheometry was used to examine the effect of adding various simple metal salts to glass-ionomer cements (Crisp, Merson Wilson, 1980). It was found that cement formation for certain glasses which react only slowly with poly(acrylic acid) could be accelerated significantly by certain metal salts, mainly fluorides such as stannous fluoride and zinc fluoride. Some non-reactive glasses could be induced to set by the addition of such compounds. 

Setchell, Teo Kuhn (1985) observed that glass-ionomer cements prepared from poly(acrylic acid) were more resistant to erosion than such cements prepared from maleic acid copolymers. This has been confirmed by Wilson et al. (1986) and by Billington (1986), even when, as in the latter case, the same glass was used in both cements. The method has been reviewed recently by Billington, Williams Pearson (1992). 

Glass-ionomers have been used in various areas of restorative dentistry since the mid 1970s. They were invented and originally described by Wilson and Kent [208], and consist of a basic glass powder and a water-soluble acidic polymer. The most widely used polymer is poly(acrylic acid), but acrylic/maleic acid copolymer is also widely used [209]. The glass powder is a complex calcium (or strontium) aluminofluorosilicate [210] that is typically at least partially phase separated. 

Zinc polycarboxylate, the first polyelectrolyte dental material, was developed and used as early as 1968 [124]. These materials are formed by the reaction of a zinc oxide powder with an aqueous solution of poly(acrylic acid). The zinc ions cross-link the polyacid chains and form a cement. A few years after the development of zinc polycarboxylate cements, Wilson and Kent introduced the first glass-ionomer cement (GIC) [125]. Glass-ionomer cements are formed... 

Composite resins consist of blends of large monomer molecules, filled with unre-active reinforcing filler. As such, they are hydrophobic, which means that they are unable to bond to the hydrophilic prepared tooth surface [1]. Glass-ionomer cements, by contrast, consist of aqueous solutions of polymeric acid, typically poly(acrylic add) and powdered reactive glass. These two components react together in an acid-base reaction, and thus cause the cement to set. These materials are hydrophilic, and therefore capable of wetting the prepared tooth surface and forming tme adhesive bonds. 

The polymers used in glass-ionomer cements are all poly electrolytes [2]. This means that they are both polymeric in character and carry electrostatic charge. It is because of this charge that they are water soluble, although when they interact with di- and... 

The polyelectrolytes used in practical glass-ionomers are polyaUcenoic acids, and two such substances are employed as the main polymer in these cements, namely the homopolymer poly(acrylic acid) and the 2 1 copolymer of acrylic acid and maleic acid. In addition, poly(vinyl phosphonic acid) has been studied as a potential cement former, but its practical use is restricted to a single brand, where it is used in a mixture with poly(acrylic acid) and effectively acts as a setting rate modifier. 

The ability of glass-ionomers to form a natural adhesive bond to the surface of the tooth is one of these material s most important clinical advantages. They were originally prepared from poly(acrylic acid), a substance chosen because of its use in the zinc polycarboxylate cement, a material known to adhere to the tooth surface [123]. The advantages of adhesion by these materials were apparent right from the start, when they were used for the repair of cervical erosion lesions and as pit and fissure sealants [124,125]. 

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